Embodiments of the present invention relates to the processing of a dielectric film on a substrate.
Dielectric films are used during the processing of substrates such as semiconductor wafers or displays. For example, dielectric films can be used as hard masks to increase the selectivity of an etch process. Dielectric films can also be used as anti-reflective coatings during the photolithographic patterning of interconnect features. Additionally, dielectric films can form component layers of features formed on substrates. For example, dielectric films with high dielectric constants can form gate dielectrics in metal gate transistors and insulators between metal electrodes in metal-insulator-metal capacitors. Dielectric films can also form protective layers in micro-electrical-mechanical system devices.
In conventional methods of depositing dielectric films by chemical vapor deposition (CVD) processes—in which a substrate is exposed to heated gases or a plasma of a gas composition—it is difficult to control or alter the chemical composition of the dielectric material being deposited. CVD processes typically rely on a chemical decomposition reaction to generate the desired dielectric material. However, CVD gases can have varying impurity levels from one batch to another. Also, CVD reactions often generate undesirable reaction byproducts as well as the desired dielectric material, since it is difficult to control the gas phase reactions in a plasma environment, thereby reducing the quality of the deposited film. CVD processes also often generate dielectric materials with stoichiometric ratios of elements that are inherent to the chemical reaction underlying the CVD process, and consequently, are difficult to control or change, because such a change would require a different chemical reaction which may not exist or may be difficult to induce. It is sometimes desirable to selectively alter the ratio of elements of a deposited dielectric film to obtain particular film properties, and to change the ratio of elements during the deposition process to obtain multilayer films.
Physical vapor deposition (PVD) processes—in which energized gases sputter material from a sputtering target which then deposits on the substrate—can be more easily altered to achieve a predefined composition of deposited dielectric material. For example, reactive gases can be added during the PVD process to deposit compounds that are mixtures of the target material and reactive gas species. PVD process can also use DC magnetrons to energize gases near the target by applying a DC voltage to the target. However, even such PVD methods can create problems when depositing dielectric films, because the target material and reactive gases can combine to create both metallic and insulating states on the surface of the target. Charged particles from the energized gases can also accumulate on the insulated portions of the target surface and eventually cause arcing within the process chamber. This is an electrical hazard and can damage chamber components or even create contaminants within the chamber by dislodging particles from interior chamber surfaces.
Thus, it is desirable to have a method and apparatus capable of depositing a dielectric film in which the ratio of elements within the deposited film can be controlled to obtain a selectively tuned stoichiometry of deposited material. It is also desirable to deposit such films with lower and more consistent levels of impurities in the deposited film. It is further desirable to have a deposition process in which deposition parameters can be controlled to achieve complex multilayered films with tunable properties.